Communication systems that transmit signals modulated according to various techniques, such as pulse shaped M-ary phase shift keying (PSK), M-ary quadrature amplitude modulation (QAM) and orthogonal frequency-division multiplexing (OFDM), typically have a peak-to-average power ratio (PAPR) that ranges from 8 dB to 12 dB. Consequently, these systems are not capable of efficient operation of their transmitter power amplifiers. For example, Class-C, Class-E and Class-F amplifier operate efficiently when biased near saturation; however, high PAPR values preclude such operation.
Pulse shaping can be eliminated to overcome the problem of a high PAPR; however, the communications waveform is spectrally unconfined and the power amplifier may be required to operate with more than five times the bandwidth of a spectrally confined waveform. For this reason, Class-A or Class-AB power amplifiers are often used in communications systems with the amplifiers significantly backed off from saturation.